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arrow of time

To extinguish your total bank of knowledge on the subject of a book by page 11 can be either a good thing or a bad thing, depending on your self esteem, your habits of curiosity or your attitude about learning. I try not to read books that I suspect will simply restate what I already know, or ones that I am predisposed to agree with. Rather I enjoy books that are a bit out of my league. I may have overshot a bit with this one.

If you have ever watched Sean Carroll’s Youtube videos, you know that his verbal speed is not much slower than 299,792,458 meters per second, which is also the known speed of light. But a book can be paused, reread, skimmed and scanned, and Carroll is one of those Richard Feynman kind of physicists that perfectly explains complex ideas that are nearly impossible for the layman to retain, much less explain to another layman. And the reader can reread as many times as it takes to get it (the pictures help, too).

The idea of time has fascinated me ever since I sat one day at a bus stop and realized that if there is no matter, there can be no time. So what is time? In an episode of Brian Cox’s excellent series The Wonders of the Universe, Cox explains that the reason things are the way they are is because it is much more likely that they would become that way than another way. Things change from an ordered state to a disordered state because there are many more different ways to be disordered than ordered. And this is crucial in the understanding of time and why it is important.

Entropy is the number of ways that the components of a system can be rearranged without a noticeable difference. As Brian Cox explains above, a pile of sand has high entropy, and a sand castle has low entropy. There is no law in physics that says the sandcastle could not be blown by the wind to form another adjacent, identical sand castle; it is only much more likely that it will not. Why is this important in relation to time? We know now that entropy always increases over time, and the only way that we really know the difference between the past and the present is because of the processes of matter changing from low entropy to high entropy. It is the reason we can’t remember the future, why we get old, why it’s very hard to unscramble an egg, why there is an arrow of time that goes in only one direction. We notice change and therefore conceptualize that change with time.